The present invention relates to a storage apparatus adapted for separately storing several graded sizes of a particulate aggregate, and which is useful in the production of an asphaltic mix.
Conventional batch type plants for producing asphaltic mix typically comprise a drum dryer for heating and drying the stone aggregate, and a vertical bucket elevator for conveying the heated and dried aggregate from the dryer to the top of a tower. The tower includes an enclosed vibrating screen assembly at the top, for receiving and segregating the aggregate by size. The segregated aggregate then drops through individual chutes to a bin section which underlies the screen assembly, and which comprises a plurality of separate bins aligned in a transverse direction, and so that each bin receives an aggregate of a predetermined average size from the screen assembly. A weigh hopper is positioned below the bins, which permits the aggregate from one or more bins to be weighed out to provide a desired mixture, as required for example for a roadway base coat or a finish coat. A mixing pugmill is positioned below the weigh hopper for mixing the weighed quantity of aggregate with hot liquid asphalt, and the bottom of the pugmill includes a gate opening, such that the contents may be dropped into an underlying truck.
The initial bin in the transverse line of bins, and which is commonly referred to as the "fines" bin, receives the relatively fine aggregate, and the aggregate becomes progressively more coarse as it is delivered into the subsequent bins at the downstream end of the screen assembly. Also, the initial fines bin typically has an open top of substantially greater dimension than that of the remaining bins, and thus the initial fines bin receives a much broader range of aggregate size than does the other bins. A longstanding problem is the fact that the finer portion of this range of aggregate size which is destined for the initial fines bin tends to find its way quickly through the associated screen while the more coarse portion takes a longer time. This results in a gradation of the aggregate within the initial fines bin, with a more fine portion of the aggregate being received in the front end of the bin and a more coarse portion of the aggregate being received in the rear end of the bin. This gradation in turn creates a problem in withdrawing the aggregate from the discharge port at the bottom of the bin, in that the coarse aggregate tends to crowd out the fine aggregate and prevents it from flowing out uniformly. Thus, when the discharge port is opened, the discharge includes surges of coarse and fine aggregate, and the discharge is not uniform. As a result, it is not possible to accurately control the size of the aggregate in the asphaltic mix being produced.
It is accordingly an object of the present invention to provide an apparatus for producing asphaltic mix and which avoids or at least significantly alleviates the above noted problem associated with conventional plants.
It is a more particular object of the present invention to provide an apparatus for producing asphaltic mix which achieves a substantially uniform discharge of both the relatively fine and the relatively coarse aggregate in the initial fines bin upon opening of the discharge port thereof, and so that the size of the aggregate in the resulting asphaltic mix can be accurately controlled.